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vector<vector<int>> havelHakimi(const vector<int>& deg) {
priority_queue<pair<int, int>> pq;
for (int i = 0; i < sz(deg); i++) pq.push({deg[i], i});
vector<vector<int>> adj;
while (!pq.empty()) {
auto v = pq.top(); pq.pop();
if (sz(pq) < v.first) return {}; //ERROR
vector<pair<int, int>> todo;
for (int i = 0; i < v.first; i++) {
auto u = pq.top(); pq.pop();
adj[v.second].push_back(u.second);
adj[u.second].push_back(v.second);
u.first--;
if (u.first > 0) todo.push_back(u);
}
for (auto e : todo) pq.push(e);
}
return adj;
}
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